OBJECTIVES: To introduce the combined South African cohorts of the International epidemiologic Databases to Evaluate AIDS Southern Africa (IeDEA-SA) collaboration as reflecting the South African national antiretroviral treatment (ART) programme; to characterise patients accessing these services; and to describe changes in services and patients from 2003 to 2007. DESIGN AND SETTING: Multi-cohort study of 11 ART programmes in Gauteng, Western Cape, Free State and KwaZulu-Natal. SUBJECTS: Adults and children (<16 years old) who initiated ART with ≥3 antiretroviral drugs before 2008. RESULTS: Most sites were offering free treatment to adults and children in the public sector, ranging from 264 to 17 835 patients per site. Among 45 383 adults and 6 198 children combined, median age (interquartile range) was 35.0 years (29.8 - 41.4) and 42.5 months (14.7 - 82.5), respectively. Of adults, 68% were female. The median CD4 cell count was 102 cells/µl (44 - 164) and was lower among males than females (86, 34 - 150 v. 110, 50 - 169, p<0.001). Median CD4% among children was 12% (7 - 17.7). Between 2003 and 2007, enrolment increased 11-fold in adults and 3-fold in children. Median CD4 count at enrolment increased for all adults (67 - 111 cells/µl, p<0.001) and for those in stage IV (39 - 89 cells/µl, p<0.001). Among children <5 years, baseline CD4% increased over time (11.5 - 16.0%, p <0.001). CONCLUSIONS: IeDEA-SA provides a unique opportunity to report on the national ART programme. The study describes dramatically increased enrolment over time. Late diagnosis and ART initiation, especially of men and children, need attention. Investment in sentinel sites will ensure good individual-level data while freeing most sites to continue with simplified reporting.